Deposition tool cleaning process having a moving plasma zone

ABSTRACT

The present invention provides, in one embodiment, a process for cleaning a deposition chamber ( 100 ). The process includes a step ( 100 ) of forming a reactive plasma cleaning zone by dissociating a gaseous fluorocompound introduced into a deposition chamber having an interior surface and in a presence of a plasma. The process ( 100 ) further includes a step ( 120 ) of ramping a flow rate of said gaseous fluorocompound to move the reactive plasma cleaning zone throughout the deposition chamber, thereby preventing a build-up of localized metal compound deposits on the interior surface. Other embodiments advantageously incorporate the process ( 100 ) into a system ( 200 ) for cleaning a deposition chamber ( 205 ) and a method of manufacturing semiconductor devices ( 300 ).

This application is a divisional of application Ser. No. 10/653,661,filed Sep. 2, 2003.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed in general to the manufacture ofsemiconductor devices, and, more specifically, to an efficientdeposition chamber cleaning process for deposition tools used in themanufacture of such devices.

BACKGROUND OF THE INVENTION

The formation of uniform layers on semiconductor substrates necessitatesthat the environment inside the deposition chamber of deposition tools,such as chemical vapor deposition (CVD) tools, be continuously monitoredand cleaned for residue build-up and contaminants. Consider, forinstance, a plasma enhanced chemical vapor deposition (PECVD) tool. Sucha tool is commonly employed to deposit material layers, such as silicondioxide (SiO₂) or fluorinated silicate glass (FSG) on a substrate, suchas a silicon wafer. It is well known that over a period of use, thematerial layers form as deposits on the walls of a deposition chamber.The buildup of these material layer deposits is undesirable because thedeposits can flake off from the chamber's interior surfaces andintroduce defects into the substrate and overlying layers and decreasethe uniformity of layers being deposited on the substrate and theoverall quality of the device.

To reduce the build-up of material layer deposits, the depositionchamber is periodically cleaned in situ, usually using afluorine-containing cleaning gas, referred to as a gaseousfluorocompound. Periodic in situ cleaning is typically done in-betweenchemical deposition procedures being performed on one or more batches ofsubstrates. In situ cleaning procedures attempt to provide a balancebetween efficient chamber cleaning in a minimum period and using aminimum amount of fluorocompound. For instance, a conventional cleaningprocedure uses a two-step process where the cleaning gas is introducedat two different rates: a high flow and a low, for the first and secondsteps, respectively. Over time, however, such cleaning procedures becomeless effective, leading to increased numbers of defective semiconductordevices being produced in the chamber. Moreover, as the yield offunctional devices produced from the chamber continues to decrease, iteventually becomes necessary to stop semiconductor device fabricationand replace the dome of the deposition chamber, thereby increasing theoverall costs of semiconductor device fabrication.

Accordingly, what is needed in the art is an efficient in situ cleaningprocess that allows the production of semiconductor devices with lownumbers of defects and thereby extend the time between dome changes ofthe deposition chamber.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, thepresent invention provides a process for cleaning a deposition chamber.The process includes forming a reactive plasma cleaning zone bydissociating a gaseous fluorocompound introduced into a depositionchamber having an interior surface and in a presence of a plasma. Theprocess also includes ramping a flow rate of the gaseous fluorocompoundto move the reactive plasma cleaning zone throughout the depositionchamber, thereby preventing a build-up of localized metal compounddeposits on the interior surface.

Another embodiment of the present invention is a system for cleaning adeposition chamber. The system includes a deposition chamber having aninterior surface and configured to perform chemical vapor depositions onsubstrates. The system further includes a controller configured toprovide a ramped cleaning process, as described above, in between thechemical vapor depositions.

In yet another embodiment, the present invention provides a method ofmanufacturing semiconductor devices. The method includes transferringone or more substrate into a deposition chamber having an interiorsurface and depositing material layers on the substrate. The methodfurther includes cleaning the deposition chamber using an in situ rampedcleaning process, as described above, when material layer deposits inthe deposition chamber reaches a predefined thickness.

The foregoing has outlined preferred and alternative features of thepresent invention so that those of ordinary skill in the art may betterunderstand the detailed description of the invention that follows.Additional features of the invention will be described hereinafter thatform the subject of the claims of the invention. Those skilled in theart should appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present invention.Those skilled in the art should also realize that such equivalentconstructions do not depart from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read with the accompanying FIGUREs. It is emphasized that inaccordance with the standard practice in the semiconductor industry,various features may not be drawn to scale. In fact, the dimensions ofthe various features may be arbitrarily increased or reduced for clarityof discussion. Reference is now made to the following descriptions takenin conjunction with the accompanying drawings, in which:

FIG. 1 illustrate by flow diagram, selected steps of one embodiment of aramped cleaning process of the present invention;

FIG. 2 presents a block diagram of one embodiment of a system forcleaning a deposition chamber according to the principles of the presentinvention;

FIGS. 3A to 3C illustrate cross sectional views of selected steps of anembodiment of a method of manufacturing a semiconductor device accordingto the principles of the present invention; and

FIGS. 4A and 4B show exemplary interior surfaces of deposition chambersafter repeated material layer depositions and in situ cleaning processesusing: (A) a conventional two-step cleaning process, and (B) a rampedcleaning process of the present invention, respectively.

DETAILED DESCRIPTION

The present invention recognizes the advantageous use of a depositionchamber cleaning process that moves a reactive plasma cleaning zonethroughout the deposition chamber versus prior art processes thatlocalize the plasma reaction to only certain zones within the depositionchamber. As a result, the cleaning processes of the present inventionsubstantially uniformly exposes the interior surfaces of the depositionchamber to the reactive plasma cleaning zone during cleaning. This, inturn, reduces the duration of exposure of any region of the interiorchamber's surface to the highly reactive species of the reactive plasmacleaning zone, thereby reducing the build up of localized metal compounddeposits inside the chamber.

The term reactive plasma cleaning zone as used herein refers to the mostdense region of reactive species that are produced by dissociation of afluorocompound in the presence of a plasma. For instance, NF₃ gas in thepresence of a high density plasma discharge dissociates to producereactive fluorine species, such as fluorine radical (F.) and nitrogenfluoride radicals (NF_(x)., x=1 or 2). Similarly, fluorocarbon gas inthe presence of such a plasma dissociates to produce reactive species,such as fluorine radical (F.) and fluorocarbon radicals (e.g., CF_(x).,x=1 to 3).

Because these species are highly reactive, they are also short lived.Thus, when fluorocompound cleaning gases are first introduced into adeposition chamber and dissociate in the presence of a plasma, thereactive plasma cleaning zone comprising a dense region or cloud ofthese reactive species, will transiently form in a localized volume ofthe chamber, and then diffuse and react with oxide deposits, the chamberwalls and each other. As new gaseous fluorocompound is introduced intothe chamber, the reactive species in the reactive plasma cleaning zoneare replenished. Moreover, by changing the flow rate at which gaseousfluorocompound is introduced into the chamber, the reactive plasmacleaning zone can be moved to different locations in the chamber, asfurther explained below.

The cleaning process of the present invention is in contrast totraditional cleaning protocols used for deposition chambers. Thetraditional view is that it is sufficient to introduce a cleaning gasat, for example, a high flow rate in a first cleaning step, and thenreduce the flow rate of the gas in a second cleaning step. It is thoughtthat the first step cleans the upper portion of the chamber, while thesecond step further cleans the walls and lower portions of the chamber.The fact that this method of cleaning is well ingrained in the field isdemonstrated by the fact that certain commercial cleaning systems areonly configured for two-step or three-step cleaning processes and arenot designed to be re-configured to implement a cleaning process such asdisclosed in the present invention.

The present invention benefited from the novel recognition that thereactive plasma cleaning zone is not uniformly distributed throughoutthe interior surface of the deposition chamber during conventional two-or three-step cleaning processes. Rather, it has been learned thatconventional in situ cleaning processes allow excessive reactions tooccur between the interior walls of the chamber and the reactive speciesof localized reactive plasma cleaning zones. This, in turn, results inthe formation of localized metal compound deposits on the interior wallsof the chamber that introduce defects into semiconductor devicesfabricated in the chamber.

As further illustrated in the example section below, consider aconventional two-step plasma cleaning process where NF₃ cleaning gas isintroduced into a deposition chamber having an aluminum dome, at twodifferent flow rates, high and low. The periodic use of such a cleaningprocess results in the formation of localized aluminum fluoride (e.g.,AlF₃) deposits inside the chamber. In particular, larger amounts ofmetal compound deposits are formed in certain regions, such as the topof the dome and near gas injectors and the chuck located at the bottomof the chamber, than in other regions of the chamber.

The localized aluminum fluoride deposits formed when using two-and threestep cleaning processes can reach thickness of between about 0 and about1000 microns. These metal compound deposits can delaminate during thedeposition of silicon oxide or fluorinated silicate glass layers ontosubstrate wafers. In particular, thermal cycling of the chamber, due tousing different radio-frequency powers during PECVD procedures fordevice fabrication, promotes delamination of these localized metalcompound deposits. Particles comprising the metal compound deposits fallonto wafers during semiconductor device fabrication and introducedefects into semiconductor devices, similar to the well known flakingoff of silicon oxide or FSG deposits, as described above. For certainfabrication processes, it has been estimated that defects from aluminumfluoride particles account for a 3 percent loss in the yield offunctional semiconductor devices.

One embodiment of the present invention is a process for cleaning adeposition chamber. FIG. 1 presents by flow diagram, selected steps ofan exemplary ramped cleaning process 100 following the principles of thepresent invention. In step 110 of the process 100, a reactive plasmacleaning zone (“reactive zone”) is formed by dissociating a gaseousfluorocompound introduced into a deposition chamber in a presence of aplasma. In step 120, a flow rate of the gaseous fluorocompound is rampedto move the reactive plasma cleaning zone throughout the depositionchamber. This, in turn, prevents a build-up of localized metal compounddeposits on interior surfaces of the deposition chamber.

In some embodiments of the ramped cleaning process, ramping of the flowrate of the gaseous fluorocompound is achieved by adjusting the flowrate according to a ramp function. In certain embodiments, the rampfunction defines a linear change in the flow rate over a cleaning time.Thus, the ramp function is (FR)_(t)=M(T)+(FR)₀, where, (FR)_(T) is theflow rate of the gaseous fluorocompound and time T, (FR)₀ is thestarting flow rate and M in the change in flow rate per unit time. Forinstance, when M is a negative number, the linear change in flow ratecorresponds to a decrease in the flow rate until the flow rate is zero,or some other predefined endpoint. In certain preferred embodimentswhere the ramp function is a linearly decreasing ramp of the flow rate,M is between about −5 and about −20 sccm/s, and more preferably betweenabout −7 and −9 sccm/s.

Of course, one skilled in the art should understand that the rampfunction is approximated by starting the flow rate at the desiredhighest value (e.g., (FR)₀) for a fraction of the total cleaning time,and then decreasing the flow rate by fixed increments and maintainingthe flow rate at the decreased value for the same fraction of time,until the desired endpoint is reached. As an example, for a totalcleaning time of 120 seconds, (FR)₀ can be started at 1000 sccm for 12s, and then decreased by 100 sccm increments to 900 sccm for 12 s, andthen decreased by 100 sccm to 800 sccm for 12 sec, etc. . . . , until aflow rate of zero is obtained. Such a cleaning protocol approximates anM value of about −8.2 sccm/s.

In other embodiments, however, the linear change in the ramp functioncorresponds to a fixed increase in the flow rate, that is, M ispositive. Using an analogous example to that given above, (FR)₀ canstart at 100 sccm for 12 s and then increases by 100 sccm incrementsuntil the flow rate of 1000 sccm is reached for 12 s, at which point theflow rate is dropped to zero, and the cleaning process is terminated orrepeated, as desired.

In yet other embodiments, the ramp function defines a nonlinear changein the flow rate of the gaseous fluorocompound over a cleaning time.Such embodiments can advantageously provide a shorter or longer cleaningperiods for certain areas of the deposition chamber, as needed. In someembodiments, it is desirable to provide a longer period of cleaning inthe upper portion of the chamber by introducing the gaseousfluorocompound at higher flow rates for a longer portion of the cleaningperiod. In such instances, the ramp function can be a higher orderpolynomial equation, such as (FR)_(t)=A(T)²+B(T)+(FR)₀, where A and Bare constants. In an alternative application, the ramp function can be asecond order polynomial, where A and B are about −0.07 s⁻² and about −1s⁻¹, respectively.

It is desirable to provide a shorter period of cleaning in the upperportion of the chamber, by introducing the gaseous fluorocompound athigher flow rates for a shorter portion of the cleaning period. In suchembodiments, the ramp function is an exponential function such as(FR)_(t)=(FR)₀·exp(N·T), where N is a constant having a negative value.An example of an exponentially decreasing flow rate as a function oftime includes (FR)₀ is about 1000 sccm and N is about −0.03 s⁻¹. Ofcourse, one of ordinary skill in the art should understand that anynumber of ramp functions could be defined or combined so as to tailorthe ramped cleaning process 100 to the particular deposition chamber ofinterest.

The scope of the present invention includes the use of any gaseousfluorocompound for cleaning deposition chambers. In certain preferredembodiments, the gaseous fluorocompound is nitrogen trifluoride (NF₃),or a perfluorocarbon such as tetrafluoromethane (CF₄), hexafluoroethane(C₂F₆) or octofluoropropane (C₃F₈), or mixtures thereof. In oneadvantageous embodiment, nitrogen trifluoride (NF₃) is used because ofits higher etch rates of material layer deposits, such as silicon oxidesor FSG deposits, lower cost and lower environmental impact, as comparedto fluorocarbons.

The gaseous fluorocarbon can be supplemented with additional cleaninggases that improve the efficient of the process 100, if so required. Forexample, the cleaning process may further include introducing oxygen(O₂) into the deposition chamber. Preferably, oxygen is introduced at aflow rate that is a fixed percentage of a flow rate of the gaseousfluorocompound. For instance, in certain preferred embodiments, the flowrate of O₂ is introduced at a flow rate that is between about 1 andabout 50 percent, and more preferably between about 5 and about 15percent, of the flow rate of the gaseous fluorocompound. Thus, incertain embodiments, the flow rate of oxygen is ramped according to thesame ramp function used to control the flow rate of the gaseousfluorocompound. In other embodiments, however, it is advantageous tointroduce oxygen at a constant flow rate, or according to a differentramp function to tailor the movement of the reactive plasma cleaningzone throughout the chamber.

In one particular embodiment of the ramped cleaning process 100, thedeposition chamber is maintained at a pressure of between about 0.5 andabout 4 Torr and more preferably between about 1 and about 3 Torr duringthe ramped cleaning process 100. In other embodiments, however, thepressure inside the chamber can be changed during the ramped cleaningprocess 100. As noted above, ramped cleaning process 100 includes thegeneration of a plasma, such as a radio frequency or microwave plasma.In the presence of a plasma, the above-described gaseous fluorocompoundand other gases are more reactive and therefore, the total timenecessary for cleaning is advantageously reduced. In still otherembodiments, the plasma is produced by applying a constantradio-frequency energy to the deposition chamber at a power of betweenabout 100 and 10000 Watts and more preferably between about 4000 and4500 Watts. In yet other embodiments, however, the strength of theplasma can be changed during the ramped cleaning process 100.

Some embodiments of the cleaning process 100 are advantageouslyintegrated as in situ cleaning processes as part of a process 130 formanufacturing semiconductor devices. In such embodiments, the depositionchamber can be part of a conventional CVD tool, such as a PECVD tool. Aswell understood by those skilled in the art, substrates, such as siliconwafers, are placed into the chamber, in step 140, and one or morematerial layers are formed on the surface of substrates, in step 150.

The chemical composition of material layer deposits that form on theinterior surfaces of the chamber during the manufacturing process 130depends on the type of deposition procedure being performed and thecomposition of the chamber. For instance, when silicon oxide and siliconnitride layers are formed on a substrate, material layer deposits inaluminum chambers are composed primarily of silicon oxides and siliconnitrides, respectively. When FSG layers are deposited, then materiallayer deposits in the aluminum chamber similarly includes siliconoxides.

As well understood by those skilled in the art, any number of indicatorscan be used to trigger the ramped cleaning process 100. In certainembodiments, the cleaning process 100 is initiated, in step 160, afterevery substrate is processed according to steps 140 and 150. In otherembodiments, however, the ramped cleaning process 100 is initiated instep 160, only when the material layer deposits in the chamber exceed apredefined limit. In some embodiments, the cleaning is commenced, forexample, when the thickness of FSG deposits inside the chamber isestimated to reach a predefined maximum, such as about 5 to about 10microns thick.

One skilled in the art should understand that the gaseous fluorocompoundand other cleaning gases serve as etchants that react with the materiallayer deposits to produce cleaning by-products. Such byproducts can beremoved from the chamber, in step 170 through gas outlets in thechamber. One skilled in the art should also understand that cessation ofthe ramped cleaning process 100 may be prompted by any number ofendpoints, in step 180. In some embodiments of the process 100, forinstance, the endpoint 180 simply corresponds to a single execution oframped cleaning according to the ramp function, as described above. Inother embodiments of the process 100, however, the endpoint 180corresponds to a change in the concentration of cleaning by-products,such as an increase in fluorine and decrease carbon monoxide, producedfrom reactions between the fluorocarbon gas and oxide deposits in thechamber.

The method cleaning process 100 may also include a step 190 of modifyinga controller to provide a ramped cleaning process controller. Suchembodiments are applicable, for instance, where the deposition chamberoriginally had a controller configured to conduct a two-step cleaningprocess. These embodiments may further include implementing the rampedcleaning process controller to execute the ramp function. In step 195,it is determined if the manufacturing process 130 should be stopped, orcontinued by repeating steps 140 and 150, if additional substrates(e.g., wafers) are to be processed.

Yet another embodiment of the present invention is illustrated in theblock diagram of FIG. 2, a system 200 for cleaning a deposition chamber205. The deposition chamber 205 has an interior surface 210 and isconfigured to perform chemical vapor deposition. The system furtherincludes a controller 215 configured to provide a cleaning processin-between the chemical vapor deposition. The cleaning process can beany of the embodiments of the ramped cleaning process of the presentinvention, such as illustrated in FIG. 1 and described above, can beused in the system 200.

In some embodiments, the system 200 includes a deposition chamber 205having one or more substrate stations 220 contained therein, eachsubstrate station 220 having one or more injectors 225. The controller215 can be configured to initiate the ramped cleaning process after eachsubstrate or batch of substrates is processed in the chamber 205. Otherembodiments of the system 200 further include a detector 230 configuredto monitor cleaning by-products of material layer deposits 235 in thedeposition chamber 205, and the controller 215 is configured to initiatethe ramped cleaning process in response to a signal 240 from thedetector 230.

In certain preferred embodiments, the detector 230 sends the signal 240to the controller 215 when cleaning by-products of the material layerdeposits 235 change by a predefined amount. In some embodiments, forexample, the detector 230 includes an optical spectrometer 245configured to measure optical emissions from cleaning by-productsproduced from a reaction between the deposits 235 and the gaseousfluorocompound. Preferably, the optical spectrometer 245 measuresoptical emissions from one or more of fluorine and carbon monoxide atwavelengths of about 704 and 483 nanometers, respectively.

In particular embodiments of the system 200, where the controller 215 isoriginally configured to conduct a two-step cleaning process, thecontroller 215 is modified to provide a ramped cleaning processcontroller 215. Such embodiments further include using the rampedcleaning process controller 215 to execute ramped function describedabove. The controller 215 may also be configured to include one or moremass flow controllers 250, 255 for introducing fluorocompounds or othercleaning gases into the deposition chamber 205. For example, in somepreferred embodiments, the controller 215 is configured to actuate theflow of cleaning gases, such as NF₃ and O₂ through a gas deliverysystem, such as an injector system 225 inside the deposition chamber205. Other gas delivery systems, such as a showerhead system could alsobe used, however. In yet other embodiments, the controller 215 is alsoconfigured to regulate a radio frequency power source 260 used togenerate a plasma inside the deposition chamber 205 during the rampedcleaning process.

The system 200 may also include a computer 265 configured to read a datafile 270 having settings, including the ramp function, for the rampedcleaning process used by the controller 215. Such settings can alsoinclude parameters, such as gas flow rates, radio frequency powersetting, chamber pressures, and the durations of particular settings.Other embodiments of the system 200 also include a computer readablemedia 275 that is capable of causing the computer 265 to produce acontrol signal 280 that causes the controller 215 to initiate the rampedcleaning process or to cease the cleaning cycle. The computer readablemedia 275 can comprise any computer storage tools including, but notlimited to, hard disks, CDs, floppy disks, and memory or firmware.

In yet another embodiment of the present invention there is presented amethod of manufacturing semiconductor devices. FIGS. 3A to 3C illustratecross sectional views of selected steps of an embodiment of a method ofmanufacturing a semiconductor device 300 according to the principles ofthe present invention. Turning first to FIG. 3A, the method includestransferring one or more semiconductor substrates 305 into a depositionchamber 310 having one or more substrate stations 315 contained therein.Preferably the deposition chamber includes a gas delivery system, suchas an injector system 320 at one or more substrate stations 315.

As shown in FIG. 3B, material layers 325 are deposited on thesemiconductor substrates 305. In certain embodiments, the materiallayers 325 are inter-level, or in other embodiments, a top level,dielectric layers 325. For example, the material layers 325 may besilicon dioxide or silicon nitride, while in other embodiments, thematerial layers 325 are FSG. Typically, the deposition is carried outusing conventional CVD or PECVD procedures, well known to those skilledin the art.

As shown in FIG. 3C, the method 300 further includes cleaning thedeposition chamber 310 using an in situ cleaning process when materiallayer deposits 330 in the deposition chamber 310 reach a predefinedthickness 335. The in situ ramped cleaning process may comprise any ofthe previously described cleaning processes of the present invention.The predefined thickness 335 can be estimated from a rate of depositingthe material layers 325 on the substrates 305. For example, in someembodiments using a TEOS process to deposit silicon dioxide layers 325on silicon wafer substrates 305, the predefined thickness 335 is atleast about 5 to about 100 microns.

In certain preferred embodiments, the method 300 further includesreplacing a dome 340 of the deposition chamber 310 when a yield offunctional semiconductor device 300 decreases below a predefined limit.In certain preferred embodiments, for example, the predefined limit isan about 2 percent yield of functional semiconductor devices, andwherein a period until said dome change is at least about 200 depositionhours.

Having described the present invention, it is believed that the samewill become even more apparent by reference to the following examples.It will be appreciated that the examples are presented solely for thepurpose of illustration and should not be construed as limiting theinvention. For example, although the experiments described below may becarried out in a laboratory setting, one skilled in the art could adjustspecific numbers, dimensions and quantities up to appropriate values fora full-scale production plant setting.

EXAMPLES

The following examples are presented to illustrate the effectiveness ofthe ramped cleaning process of the present invention as compared to aconventional two-step cleaning process. A single-chambered HDPCVD tool(Novellus Sequel System, San Jose, Calif.) having one substrate stationwas used. For test purposes, about 4500 Angstrom thick layers of FSG,comprising about 4.5 percent fluorine and balance silicon dioxide, weredeposited on silicon wafers using a conventional HDPCVD process. Thetool was configured to run an intermittent in situ cleaning processesbetween every 6 micron deposition of FSG.

For illustrative purposes, the results for two in situ cleaningprocesses are compared: a conventional two-step cleaning process and aramped cleaning process of the present invention. For both cleaningprocesses, the pressure inside the chamber was maintained at about 2Torr and the radio-frequency power used for plasma generation was about4300 Watts. The flow rate of NF₃ (FR-NF₃) and O₂ (FR-O₂) and theirdurations (Time) are summarized in TABLE 1. TABLE 1 Time (seconds)FR-NF₃ (sccm) FR-O₂ (sccm) Two-Step Cleaning Process (prior art) ˜190˜1000 ˜100 ˜104 ˜100 ˜10 Ramped Cleaning Process ˜36 ˜1000 ˜100 ˜36 ˜900˜90 ˜36 ˜800 ˜80 ˜36 ˜700 ˜70 ˜36 ˜600 ˜60 ˜36 ˜500 ˜50 ˜36 ˜400 ˜40 ˜36˜300 ˜30 ˜36 ˜200 ˜20 ˜36 ˜100 ˜10

The plurality of NF₃ and O₂ flow rates used in the ramped cleaningprocess approximated a linearly decreasing ramp function having a slopeof about −8.3 sccm/sec. The duration of the plurality of flow rates wasselected so as to provide the deposition chamber with the same volume ofexposure to NF₃ as in the two-step process (e.g. 190×1000+104×(100) forthe two-step process).

In order to perform a ramped cleaning process on the Novellus SpeedSystem, it was necessary to reconfigure the software program thatcontrols the two-step cleaning process originally provided with thesystem, into a ramped cleaning process. In particular, new parameters tocontrol the flow rates of NF₃ and O₂ and the duration of the pluralityof low rates to define the linear decreasing ramp function were created.An example of a portion of a reconfigured program containing the rampedcleaning process is presented in TABLE 2. TABLE 2 STEP 19 of 40: (STARTCLEAN STEP 4) EXECUTE: hen3ry (timeout, 30 sec)  Device DescriptionAction  adp1 Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2Crossover.  Open Valve  mfc2 Oxygen MFC   SetFlow(O2-4)  mfc3 NitrogenTrifluoride  SetFlow(NF34)  gen1 SCVD HF RF Generator SetGenPower(hprf) ENDING CONDITIONAL: (loop delay, 100 msec)  adp1 Throttle ValveIsPressureInPercent(20)  AND OBJC   csk2 STEP 20 of 40: (PERFORM CLEANSTEP 4) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-4)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 21 of 40: (START CLEAN STEP 5)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O2-5)  mfc3 Nitrogen Trifluoride SetFlow(NF35)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle ValveIsPressureInPercent(20)  AND OBJC   csk2 STEP 22 of 40: (PERFORM CLEANSTEP 5) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-5)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 23 of 40: (START CLEAN STEP 6)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O2-6)  mfc3 Nitrogen Trifluoride SetFlow(NF36)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle Valve IsPressureInPercent(20)  AND OBJC   csk2 STEP 24 of 40: (PERFORM CLEANSTEP 6) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-6)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 25 of 40: (START CLEAN STEP 7)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O2-7)  mfc3 Nitrogen Trifluoride SetFlow(NF37)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle Valve IsPressureInPercent(20)  AND OBJC   csk2 STEP 26 of 40: (PERFORM CLEANSTEP 7) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-7)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 27 of 40: (START CLEAN STEP 8)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O2-8)  mfc3 Nitrogen Trifluoride SetFlow(NF38)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle ValveIsPressureInPercent(20)  AND OBJC   csk2 STEP 28 of 40: (PERFORM CLEANSTEP 8) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-8)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 29 of 40: (START CLEAN STEP 9)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O2-9)  mfc3 Nitrogen Trifluoride SetFlow(NF39)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle ValveIsPressureInPercent(20)  AND OBJC   csk2 STEP 30 of 40: (PERFORM CLEANSTEP 9) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF-9)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2 STEP 31 of 40: (START CLEAN STEP 10)EXECUTE: hen3ry (timeout, 30 sec)  Device Description Action  adp1Throttle Valve SetAdaptorPressure(hppr)  vl47 NF3-O2 Crossover.  OpenValve  mfc2 Oxygen MFC   SetFlow(O210)  mfc3 Nitrogen Trifluoride SetFlow(NF10)  gen1 SCVD HF RF Generator SetGenPower(hprf)  ENDINGCONDITIONAL: (loop delay, 100 msec)  adp1 Throttle ValveIsPressureInPercent(20)  AND OBJC   csk2 STEP 32 of 40: (PERFORM CLEANSTEP 10) EXECUTE: hen3ry (timeout, 300 sec)  Device Description Action clk2 SetTicks(HF10)  ENDING CONDITIONAL: (loop delay, 100 msec)  clk2NOT IsTicksExpired  AND OBJC   csk2

FIGS. 4A and 4B show exemplary interior surfaces of the dome of thedeposition chamber after about 100 FSG deposition hours and intermittentin situ two-step or ramped cleaning processes, respectively. As shown inFIG. 4A, the dome of the chamber that was subjected to the prior arttwo-step cleaning process had several dark rings corresponding tolocalized AlF₃ deposits at the top and bottom of the dome (arrows 1 and2, respectively) in particular. The most prominent AlF₃ deposits areestimated to have thicknesses of about 0 to about 1000 microns. Incontrast, as shown in FIG. 4B, the dome of the chamber that received theramped cleaning process provided by the present invention did not haveany prominent dark rings, signifying the absence of localized AlF₃deposits.

As a further comparison of the ramped and two step cleaning processesdescribed in TABLE 1, the results of a marathon session of FSGdepositions and intermittent in situ cleaning processes were compared.When using the prior art two-step cleaning process, it was found thatafter about 200 FSG deposition hours, it was necessary to change thedome of the deposition chamber. A dome change was necessitated becauseeither the in-line defect density step increases or a yield offunctional semiconductor device decreases below a predefined limit. Asan example, in certain semiconductor device manufacturing processes thepredefined limit is about 2 percent yield of function semiconductordevices. In contrast, when using the ramped cleaning process of thepresent invention, a dome change was not indicated until about 400 FSGdeposition hours.

Although the present invention has been described in detail, one ofordinary skill in the art should understand that they can make variouschanges, substitutions and alterations herein without departing from thescope of the invention.

1. A process for cleaning a deposition chamber, comprising: forming areactive plasma cleaning zone by dissociating a gaseous fluorocompoundintroduced into a deposition chamber having an interior surface and in apresence of a plasma; and ramping a flow rate of said gaseousfluorocompound to move said reactive plasma cleaning zone throughoutsaid deposition chamber, thereby preventing a build-up of localizedmetal compound deposits on said interior surface.
 2. The process asrecited in claim 1, wherein said ramping is achieved by adjusting saidflow rate according to a ramp function.
 3. The process as recited inclaim 2, wherein said ramp function defines a linear change in said flowrate over a cleaning time.
 4. The process as recited in claim 2, whereinsaid linear change corresponds to a decrease in said flow rate untilsaid flow rate is zero.
 5. The process as recited in claim 2, whereinsaid ramp function defines a nonlinear change in said flowrate over acleaning time.
 6. The process as recited in claim 1, wherein saidgaseous fluorocompound is selected from the group consisting of:nitrogen trifluoride (NF₃); tetrafloromethane (CF₄); hexafloroethane(C₂F₆); and octofluoropropane (C₃F₈).
 7. The process as recited in claim1, further includes introducing oxygen (O₂) into said depositionchamber.
 8. The process as recited in claim 7, wherein said introducingof (O₂) is at flow rate that is a fraction of a flow rate of saidgaseous fluorocompound.
 9. The process as recited in claim 1, whereinsaid deposition chamber is maintained at a pressure of between about 0.5and about 4 Torr.
 10. The process as recited in claim 1, wherein saidplasma is produced by applying radio-frequency energy to said depositionchamber at a power of between about 100 and 10000 Watts.